The central focus of this grant application is to utilize pathophysiological manipulations to attempt to overcome the radiation resistance associated with transient (acute) and diffusion-limited (chronic) tumor hypoxia. Investigations will evaluate the effects of changes in hemoglobin (Hb) affinity for oxygen (O2) and/or tumor blood flow on tumor response to radiation. Hb affinity will be altered by the direct administration of agents which shift the Hb-02 dissociation curve or the transfusion of biochemically modified erythrocytes into tumor-bearing recipients. Tumor blood flow will be manipulated through the administration of the agents flunarizine and nicotinamide. Changes in tumor blood flow will be monitored using a variety of techniques including laser Doppler flowmetry, and the relationship between blood flow changes and radiation sensitivity will be established. To study whether specific manipulations of tumor oxygenation are producing the desired effects at the microregional level, intravascular HbO2 saturations distributions will be determined cryospectrophotometrically. Additionally, dual-staining procedures with Hoechst 33342 and DiOC 7(3) will be used to determine the relative fraction of vessels involved in transient perfusion. These studies initially will utilize the rodent KHT and SCCVII tumor models since chronically hypoxic cells dominate the former while acutely hypoxic cells can be demonstrated in the latter. For comparison, more limited experiments in human ovarian tumor xenografts also are proposed. Xenograft studies are of particular interest given the recent. controversy concerning the activity of vasoactive -agents in human versus rodent tumor models. It also is our objective to evaluate in these tumor models the therapeutic potential of combining therapies directed at the different types of hypoxia. Those conditions leading to the greatest antitumor activity will be evaluated using fractionated dose radiotherapy protocols. These investigations should improve our understanding of tumor hypoxia and may have implications for strategies aimed at overcoming hypoxia-mediated treatment resistance by specifically targeting acute and chronically hypoxic cells.